What we are hearing from countries that were first to successfully inoculate most of the population is that, after 6-8 months, people who are double vaccinated are in hospital with severe covid symptoms. In Israel, where the first to be vaccinated were older adults, that demographic group was the first to experience so many "breakthrough" cases that breakthrough was the wrong term. Since then, what is evident is that breakthrough cases occur in people who had been double vaccinated 6-8 months earlier.
Per the CBC article I linked in comment #841, the "rate of infection has been found to be higher in people vaccinated back in January, compared with people who were vaccinated in April ... "In simple words:
That protection against infection is waning over time."
This is not a situation where, 8 months after double vaccines, immunity is the same as it was 4 months earlier. This appears to be a situation where people who are double vaccinated can become very ill with the Delta virus 6-8 months after vaccinations. In Israel, 60% of hospitalized covid patients are double vaccinated 6-8 months prior to becoming ill.
"Israel has among the world’s highest levels of vaccination for COVID-19, with 78% of those 12 and older fully vaccinated, the vast majority with the Pfizer vaccine. Yet the country is now logging one of the world’s highest infection rates, with nearly 650 new cases daily per million people. More than half are in fully vaccinated people, underscoring the extraordinary transmissibility of the Delta variant and stoking concerns that the benefits of vaccination ebb over time.
...
What is clear is that “breakthrough” cases are not the rare events the term implies. As of 15 August, 514 Israelis were hospitalized with severe or critical COVID-19, a 31% increase from just 4 days earlier. Of the 514, 59% were fully vaccinated. Of the vaccinated, 87% were 60 or older. “There are so many breakthrough infections that they dominate and most of the hospitalized patients are actually vaccinated,” says Uri Shalit, a bioinformatician at the Israel Institute of Technology (Technion) who has consulted on COVID-19 for the government. “One of the big stories from Israel [is]: ‘Vaccines work, but not well enough.’”
Aug 16, 2021
AAAS
Sep 01, 2021
https://www.cbc.ca/news/world/israel-covid-delta-variant-booster-1.6159472